Focal plane arrays (FPAs) refer generally to a class of detectors that have more than one row of detectors and one line of detectors. There are many types of FPAs, and examples include avalanche, industrial, high speed, adaptive, and infrared FPAs. A linear array is a row of individual detectors similar to those found in a facsimile machine or a document scanner. Adaptive FPAs (AFPA) are high-performance FPAs that are widely tunable across the relevant wavebands in, e.g., the infrared (IR) spectrum and enable multispectral imaging. An adaptive focal plane array includes short-wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR) bands. An infrared FPA consists of a number of IR sensors held together. An industrial focal plane array includes special features such as low-light levels, anti-blooming/integration control, correlated double sampling, and extended blue response.
There are several ways in which FPAs function. An FPA is typically constructed with on-chip signal processing and contained within the space of the detector area. Scintillating fiberoptic cathode and anode plates can be used to detect gamma-produced electrons. Modern IR FPAs are based on indium gallium arsenide (InGaAs) technology. A high speed focal plane array provides excellent performance at high-speed and low-light levels. An FPA can be specified according to its size and area. Focal plane arrays can be designed and manufactured according to various industry specifications.
Focal plane arrays are used in many applications. Examples include astronomical imaging, aerial reconnaissance, aerial mapping, spectrographic analysis, star tracking, missile seekers, dental and medical radiography, machine vision, x-ray diffraction, and other state-of-the art military, industrial, and scientific measurement applications. For instance, Moderate Resolution Imaging Spectroradiometer (MODIS) deployed in NASA's Earth Observing System (EOS) a decade ago had 36 spectral bands over 0.4-14.4 pm wavelength. Current state of the art hyper-spectral radiometers being developed employ either Fourier Transform Spectrometers (FTS) or Push-broom radiometers in combination with optical filters, offering over 100 spectral bands. However, they can be complex, expensive, and power-hungry. Conversely, achieving multi- or hyper-spectral 2-dimensional starring FPAs has been extremely challenging; current state of the art FPAs are limited to no more than three colors, using either HgCdTe photodetectors or Quantum Well Infrared photodetectors (QWIPs). A vertical integration of wavelength-selective QWIPs or HgCdTe detectors in a 3D cube configuration could enhance its spectral response to multi-color. However, challenges exist in material growth capability, spectral resolution at pixel, and also Read-Out circuitry and state of the art power dissipation. Importantly, none of the current SOA imagers/FPAs offer the functionality for continuously tuning or programming at the pixel levels, which could be important for imaging.
What is now needed are improved methods and apparatus for FPA imaging that offer improved performance in changing environments. The embodiments of the present disclosure answer these and other needs.